The quality of beverages is measured by different parameters, such as flavour stability, biological purity and physico-chemical stability, wherein the latter is one of the most important for beer. The physico-chemical or colloidal stability describes the occurrence of non-biological haze in bottled beverages, such as beer. This haze is mainly caused by polyphenols and proteins, which are able to react to larger molecules via hydrogen bridges. The haze-forming proteins are believed to have Mw within the range of 30-60 kDa, although the range may differ depending on the source. When removing proteins with Mw above 120 kDa, the head retention of the beer decreases. Members of the polyphenol group are, inter alia, tannins and anthocyanogens which measured separately can be used as indicators for beer stabilization. To increase the beer's stability it is usual to partially remove the polyphenols, the proteins or both by using various agents and methods. The normally desired shelf life for stabilized beer is about 6 months, with variations for different countries and/or kinds of beer.
Stabilization and clarification of beverages are two terms that sometimes are used interchangeably and sometimes are used distinct concepts. In a strict sense clarification refers to the removal of haze and particulate matter that are at hand in a given beverage while stabilization refers to the removal of potentially haze-forming substances in order to render haze formation more difficult. In the context of the present invention the two terms shall be interpreted in a strict sense.
The amount of haze-forming substances and their tendency to form haze depends on several factors. See the experimental part. Each beer, for instance, is unique in composition depending on the brewery's selection of process variables, quality of hop and barley etc. This means that an acceptable level of stability/stabilization as measured by commonly accepted tests may vary between type of beer and/or brewery. In connection with the invention fixed limits for stabilization are therefore difficult to set. As a general guideline it can be said that stabilization has occurred when a value for a test measuring both haze-forming proteins and polyphenols has been changed at least 10% towards stabilization as a consequence of employing the invention. This means that a similar change or even lower change may apply to tests measuring proteins and polyphenols separately. The goal with stabilization is not to remove all haze forming proteins and/or polyphenols, because this might easily also affect the character of a specific beverage.
Background Publications
The problems with haze-causing substances in beverages have been known for several years and a number of solutions for removal thereof have been suggested.
The most common way to remove polyphenols from beverages is to use polyvinyl pyrrolidone, PVPP. Before addition to the beverage, PVPP has to be mixed with water to form a slurry. PVPP is added to the storage tank or dosed into the beer stream before the beer filter and filtered out with other haze particles. PVPP is available in two qualities: single use and re-usable differing in particle size.
From SU 1 451 159 a process is known for beer stabilization using an ion exchange sorbent for removing polyphenols. In this process, the beer is warmed to 65-75.degree. C., and a strongly basic macro crosslinked sorbent (anion exchanger) based on copolymers of styrene and 4% divinyl compound containing functional quaternary trimethylamine groups is added. This hydrophobic sorbent is added to beer in amounts ensuring the removal of 25-30% of the polyphenols, stirred, left to stand 2-3 min., and the beer is decanted. The sorbent has a polyphenol sorption capacity of 18-19 mg/g, can be reused for at least ten times, and is regenerated with 5 parts per volume water at 45-50.degree. C.
From Rep. Res. Lab. Kirin Brew. Co. (1972), No. 15, 17-24 an anion exchanger (Dowex 1.times.4 resin) is used for fractionation of polyphenols in beer. First the polyphenols are extracted from beer, such as by ethyl acetate, then this extract is subjected to anion exchange chromatography for the purpose of fractionating the polyphenols into several groups for further studies. Thus, the anion exchanger is not used for the stabilization of beverages.
In Europe, one of the most common ways to remove proteins from beer is by using silica which has in be prepared to a slurry with water. The silica gel is added to the storage tank or is constantly dosed into the beer stream before the beer filter. The silica gel is filtered out with other haze particles and is discarded after use.
Another widely used method to remove proteins is by using tannic acid. After preparing a solution of tannin and water, the tannin is added to the storage tank or is constantly dosed into the beer stream before the beer filter. The tannin is filtered out with other haze particles and is wasted after use.
Also, there exists alternative methods for removing proteins from beverages containing haze-forming substances, such as by using proteolytic enzymes or bentonite.
The fact that the widely used silica gel and tannins are not re-usable, makes them substantial contributors to environmental pollution.
During the priority year the Swedish Patent Office has issued an International Search Report citing the following publications:
a. U.S. Pat. No. 4,100,149 that deals with the removal of proteins from beer and other beverages in order to accomplish, for instance, a clarified beer. The adsorbent used is built up of polymer coated inorganic particles. The polymer carries ion exchange groups. The experimental part focuses on coated silica particles, and it is not clear if the effect achieved is due to the silica, polymer coat or charged groups. PA1 b. EP-A-166,238 deals with neutralizing the bacteriostatic activity of polyphenols in fruit juices by addition of an agent that may or may not have ion exchange groups. PA1 c. Hughes, Food Technology in New Zealand, 10(30) (1985) suggests that cellulosic ion exchangers could be used to stabilize beer because they are known to adsorb proteins. PA1 d. U.S. Pat. No. 4,288,462 suggests that a filter element charged with anionic colloidal silica can be used for removing haze and haze-forming proteinaceous substances in beverages, such as beer. PA1 e. U.S. Pat. No. 3,623,955 concerns removal a certain enzyme from beer. PA1 f. U.S. Pat. No. 3,940,498 suggests to use an acid treated synthetic magnesium silicate for the simultaneous removal of undesireable proteins and polyphenols from beverages such as beer. PA1 g. WPI acc. no. 89-212564/29 is the same as SU 1,451,159 which has been discussed above. PA1 h. WPI acc. no 81-81725D (=DD-A-150,078) suggests the use of particulate hydrophobic material exhibiting groups capable of H bridge formation, ion exchange, chemisorption or chelation for the removal of turbity-forming materials from drinks, including beer. PA1 i. WPI acc. no. 81-15897D (GB-A-2,056,485) suggests using positively charged particles for removing substances causing cloudiness in beverages (wine, beer, fruit juices etc). The charge has been introduced by treating the particles with a cationic polyamide-polyamine epichlorohydrin synthetic material. When contacted with the beverage the particles provoke precipitation that later can be removed by filtration. PA1 j. WPI acc. no. 77-09751Y (=GB-A-1,499,849) suggests to remove haze precursors in beverages by the use of cation exchangers based on hydrophobic matrixes.
Some additional publications are: